Oxidation of aromatic hydrocarbons to phenols



Dec. 15, 1953 w. H. REEDER m 2,662,923

OXIDATION OF AROMATIC HYDROCARBONS TO PHENOLS Filed Jan. 8, 1951 AIR 1SULFUR DIOXIDE aauzeus DISCARD 14 g fig 52 GASES REACTOR\ j0 SULFUR010x105 11 coucemamme PLANT l' I I l z7 l l l l coouua E la-6:) MEDlUMQ! 22 HYDRO CARBON muse 5EPARATOR\ INVENTOR.

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Patented Dec. 15, 1953 OXIDATION OF AROMATIC HYDROCARBONS TO PHENOLSWilliam H. Reader HI, Olean, N. Y., assignor, by rnesne assignments, toDresser Operations, Inc.,- Whittier, Calif., a corporation of CaliforniaApplication January 8, 1951, Serial No. 204,878

. 19 Claims.

The present inventionrelates to the limited oxidation of aromatichydrocarbons for the formation of oxygenated compounds, particularlyphenols. This application is a continuation-inpart of my priorapplication Serial No. 676,469, filed June 13, 1946, now abandoned infavor of continuation application Serial No. 278,423, filed March 25,1952'. v

In my aforesaid prior'application, it has been disclosed thathydrocarbons, including aromatic hydrocarbon benzene, can be convertedin good yields to oxygenated compounds by using, under the conditionstherein set forth, the sulfur oxides,

sulfur trioxide, sulfur dioxide, ormixtures there-.

of, admixed with oxygen orv air, as the oxidizing agent, employing acontact mass comprising an adsorptive material alone or carrying saltsor oxides of metallic elements of the Ib periodic grou and of thetransition elements and mixtures thereof. It was pointed out that insuch processes, conducted in the vapor phase for the limited oxidationof hydrocarbons to yield oxygenated compounds, a mixture of sulfurdioxide and oxygen in which the oxygen is present in a minor proportionmay be used as the oxidizing agent.

In carrying out the process of the present invention, a vapor phasemixture of an aromatic hydrocarbon, sulfur dioxide and oxygen togetherwith suitable inert diluents, if desired, such as nitrogen, carbondioxide or the like, is caused to react at a temperature in the range ofabout 239 C. to 600 C., the effluent reaction gases being then subjectedto condensation or stripping for the removal of phenols and otherreaction products. The process can be conducted as a single passoperation. However, since'in some cases it may be desirable to operatewith a low conversion per pass to secure maximum yields, the effluentgases, after removal of the oxygenated products, may be recycled.Aromatic hydrocarbon, sulfur dioxide and oxygen are then supplied to therecycled gases in order to maintain a substantially constant compositionof the mixture entering the reaction zone.

The present process is applicable to the treatment of aromatichydrocarbons, particularly the mononuclear aromatic hydrocarbons likebenzene, toluene and xylenes. The selected hydrocarbon must be capableof existing as a vapor at the reaction temperature and pressure.principal products resulting from the treatment are the correspondingphenols and, in the case of aromatic hydrocarbons having aliphatic sidechains, the corresponding aldehydes, ketones, and carboxylic acids inaddition to the phenols,

The

The process of this invention generally is 5 markedly improved when themixture of react ant vapors is made to react while in contact with amass of solid adsorptive material. Adsorptive materials of widelyvarying types may be used and it appears that an importantcharacteristic from the standpoint of the'desired reaction is theirporous, adsorptive character rather than their specific chemicalcomposition, although some variations in behavior may result from theylatter. Adsorptive materials that may be employed include activatedcarbonaceous material, such as activated charcoal; porous siliceousmaterial, such as silica gel, fullers earth, kieselguhr, aluminumsilicates and magnesium silicates; and aluminum oxides such as activatedalumina and bauxite. It will be appreciated that in some cases,particularly of natural minerals, the adsorptive materials may betreated preliminarily with a strong acid like sulfuric acid to increasetheir porosity and improve their adsorptive character.

The beneficial influence of the adsorptive contact mass on theconversion and/or ultimate yield of the desired reaction is oftenenhanced by the addition of catalyst promoters to the adsorptive contactmass. Metallic salts or oxides which act as catalyst promoters may bedeposited on the adsorptive material to increase the effectiveness ofthe limited oxidation of aromatic hydrocarbons and to decrease theproduction of the undesired oxides of carbon. Suitable for this purposeare the salts and oxides of the elements of the Ib periodic group and ofthe transition ele ments and mixtures thereof. The transition elementsinclude the metals Sc, Ti, V, Cr, Mn, Fe,- Co and Ni in the 4th longseries; Y, Zr, Cb, Mo, Ma, Ru, Rh and Pd in the 5th long series; La, ccand the other rare earths, Hf, Ta, W, Re, Os, I1 and Pt in the 6th longseries, and Ac, Th, Pa and U in the 7th series. It will be noted that inthe long period arrangement of the elements and in the Bohnclassification the elements of the II) group, viz., Cu, Ag and Au,follow immediately the transition elements in their respective seriesand sharewith them the property of variable valency." See, for example,Ephraim, Inorganic Chemistry, 4th Ed., Revised, New York, 1943, pages 25and 29.

When the metallic salts are employed, soluble salts of the selectedmetals may be dissolved in water andthe resulting solution thoroughlymixed with the adsorptive material, which is then dried and heated ashereinafter described. The particular salt or compound which is employeddoes not appear to affect the reaction.

Thus, chlorides, nitrates, sulfates, acetates or formates or othersoluble salts of the metals may be employed, providing they aresufficiently soluble to permit of securing the desired proportion of themetallic salt or salts in the adsorptive material. In general, the.inorganic salts are preferred, since they do not leave a carbonaceousresidue when the mixture with the adsorptive material is heated to driveoff moisture and to activate the mixture, or during reaction. The amountof metallic compound incorporated into the ad.- sorptive material issuitably from about 1% to about 35%, preferably fromyabout 2% to about15%, based on the weight. of adsorptive material. The oxides or otherinsoluble compounds of the metal selected may be. precipitated in. theadsorptive material, if desired.

Irrespective of whether or not the adsorptive material contains ametallic catalyst promoter, its effectiveness may frequently beincreased by a preliminary heat treatment or activation, which may becarried out either before. or after the catalyst has been placed in thereaction chamber in which it is to be used. This treatment may beeffected by heating the adsorptive material, with or without promoter,to a high temperature of the order of 400 to 600 C. or higher. Theoptimum temperature of activation for each adsorptive material orcatalyst combination may be selected on the basis of prior tests. Goodresults are secured by heating the contact mass whilev passing incontact therewith a stream of air, of sulfur oxides, of the hydrocarbongas to be oxidized, or of mixtures thereof, providing of course, that ifa hydrocarbon is present, the activation temperature is below thecracking temperature, of the hydrocarbon. Only a short period of heattreatment is usually required, say /2 to 1 hour.

The partial oxidation of an aromatic hydrocarbon to produce a phenol isconducted in accordance with this process by charging the aromatichydrocarbon, sulfur dioxide and oxygen into a reaction zone maintainedat a temperature of about 230 to 600 (1., preferably about 350 to 550 C.Advantageously, the reaction is effected in the presence of anadsorptive contact mass, particularly one containing a catalystpromoter. Since the partial oxidation is exothermic and sensitive totemperature rises, it is advisable to maintain the concentration ofoxygen in the total feed stream to the reaction zone within the range ofabout 2% to 20% by volume, preferably within the range of about 5% to byvolume. Stoichiometry will indicate the quantity of aromatic hydrocarbonthat should be in the feed stream relative to the oxygen. For instance,the partial oxidation of benzene to phenol:

shows that benzene should be used in a volume ratio of the order of twovolumes of benzene to each volume of oxygen. The third essentialcomponent of the feed stream is sulfur dioxide and to achieve theresults of this process it is necessary that at least one volume ofsulfur dioxide be present for each volume of oxygen in the total feedstream. In general, a volume ratio of the order of 1.5 volumes of sulfurdioxide per volume of oxygen will give very satisfactory results. It isthus seen that the control of the composition of the total feed streamto the partial oxidation zone is made to revolve around the oxygen concentration (by volume) of that stream. To illustrate, in convertingtoluene to cresol, the oxygen concentration may be set at 7% by volumeof the total feed stream; then, the sulfur dioxide may be 11% by volumeof that stream (SOz/Oz approximately 1.5) and the toluene may be 15% byvolume of that stream. However, the foregoing figures account for only33% by volume of the total feed stream; the remaining 67% is made up ofinerts.

For the purposes of this invention, inerts may be the strictly inertgases like nitrogen and carbon dioxide oran excess of the aromatichydrocarbon or of sulfur dioxide. While both the aromatic hydrocarbonand sulfur dioxide are essential components of the feed stream suppliedto the reaction zone, either or both of these components when used inexcess of the proportions indicated by the oxygen in the total feed maybe part or all of the "inerts in the total feed. Inasmuch as when theoxygen is consumed the reaction can; no longer go forward, it is obviousthat excess sulfur dioxide and/or aromatic hy-. drocarbon is to allintents and purposes inert. To complete the illustration commencedherein!v before, the 67% by volume of inerts may be entirely nitrogenand/or an excess of toluene. If toluene was to provide all of theinerts, the total feed would have a volume composition of 7% of oxygen,11% of sulfur dioxide and 82% (15+6'l) of toluene.

-by decreasing the chances of developing runaway hot spots in thereaction zone.

Since the process of this invention is carried out with all thecomponents of the feed stream in the vapor state when they are in thereaction zone, it is clear that mention herein of volumes or volumepercentages of feed componennts refers to vapor volumes under comparableconditions.

An elevated pressure in the reaction zone is often desirable because itreduces the size of the reactor and the power to recycle effluent gasesissuing from the reactor. It is also observed that an elevated pressuregenerally lowers the reaction temperature and this is advantageous withan exothermic reaction of the type contemplated by this inventionbecause the lower the operating temperature the easier it is to controlit within narrow limits. While pressures of 600 p. s. i. g. and highermay be used, the pressure range of about to 300 p. s. i. g. is usuallypreferred. In any given reaction, it is understood of course that thereaction pressure should not be so high that liquefaction occurs withinthe reaction zone under operating conditions,

The eflluent gases from the reaction zone containing the desiredoxygenated compoundsas well as sulfur oxide, oxides of carbon, watervapor and unconverted aromatic hydrocarbon may be passed throughsuitable cooling means whereby condensation of water, hydrocarbon, etc.is effected. In general, the desired oxygenated products will be foundto be divided between aqueous and hydrocarbon phases of the resultingcondensate. The two liquid phases are subjected to suitable treatment,e. g., distillation or extract o for the reco e o th desired products-Alternatively, the reaction gases may be brought in o con ct with a lqui Scrubbing medium which pr fe entiall absorbs the de u s which. nturn, are h n se a from the scrubbing medium by distillation.

An illust at ve o th s i ye tign is aeeaoas represented diagrammaticallyin the accompanying drawing.

Reactor l comprises two concentric tubes forming an inner reaction zoneI l which desirably contains a bed of particulate contact material orcatalyst and an annular cooling jacket l2 for regulating the reactiontemperature within zone H, Jacket 12 is supplied with a cooling mediumthrough inlet 13 and the warmed medium is withdrawn through outlet [4.Feed line I which is connected to reaction zone H is supplied withoxygen, e. g., air, and aromatic hydrocarbon, e. g., benzene, by lines16 and II, respectively, while line [8 furnishes sulfur dioxide. Thesereactants are generally preheated before entering reaction zone I I. Themixed reactants flow through reaction zone ll maintained at reactionconditions so that the aromatic hydrocarbon is partially oxidized to aphenolic compound. The reaction gases pass from reaction zone H throughline [9 into condenser 20. Condensate and residual gases flow fromcondenser 20 through line 2| into separator 22 wherein the condensateforms water and hydrocarbon phases. The water phase is withdrawn throughline 23, the hydrocarbon phase through line 24 and uncondensed gasesthrough line 25. The two liquid phases with drawn through lines 23 and24 are treated, e. g., by distillation or extraction, to recover theunconverted aromatic hydrocarbon and oxygenated product values therein.Any recovered aromatic hydrocarbon may be recycled to reaction zone I 1by way of lines I! and 15. The gaseous stream passing through line 25 isrich in sulfur dioxide and it is highly desirable to recycle this sulfurdioxide to reaction zone II and thus curtail the quantity of freshsulfur dioxide that is supplied to line [8 from an extraneous source.The gaseous stream containing sulfur dioxide may be recycled withoutfurther treatment by pump 26, line 21, valved branch line 28 and line 29which discharges into sulfur dioxide supply line l8. When the sulfurdioxide is thus recycled to reaction zone I I, a portion of the gaseousstream passing through line 25 is ventedthrough valved line 30 toprevent the build-up of inertslike nitrogen and carbon oxides in thereaction system. Obvi ously, some sulfur dioxide will be lost with thevented stream and the lost sulfur dioxide will be replaced by freshsulfur dioxide supplied by line 18. Alternatively, it may be advisableto decrease the loss of sulfur dioxide. In such case, the valved lines30 and 28 are closed and all of the gaseous stream containing sulfurdioxide is passed through pump 26, line 21 and valved branch line 3|into concentrating plant 32 wherein by absorption or low-temperaturefractionation or other known methods the sulfur dioxide is concentratedor separated from the other gases. The separated sulfur dioxide thenflows through lines 33, 29, I8 and I5 into reaction zone I I. The smallloss of sulfur dioxide which usually remains in the discard gases ventedthrough line 34 is made up by fresh sulfur dioxide introduced by supplyline [8.

The following examples are further illustrative of operations conductedin accordance with the present invention:

Example 1 In an operation carried out at a pressure of 270 p. s. i. g.and a temperature of 500 C., the adsorptive catalytic material employedwas alumina of 4 to 8 mesh containing 10% by weight of cobalt sulfateand 2.8% by weight of silver nitrate. The catalyst-containing reactionzone was a stainless steel tube with an internal crosssectional area of0.1075 sq. in. and contained 4 ml.

catalyst. The rate of total reactant feed was 10.92 gram mols per hourand the gasiform reactant feed contained,by volume, 22.9% benzene, 18.1%sulfur dioxide, 11.8% oxygen and 47.2% nitrogen. The percent conversionper pass of the benzene to phenol on a molar basis was sub' stantially10% and the yield ofphenol based on the mols of benzene consumed wasslightly over 77%.

1 Similar operations were conducted at various temperatures throughoutthe range heretofore referred to and at a pressure or 270 p. s. i. g.with effective yields of phenol. Thus, at 480 C. under otherwise similarconditions of operation with substantially the same composition of theentering reactant gas, the percent conversion of benzene to phenol perpass through the reaction zone on a molar basis was 8.6% and the yieldof phenol on the benzene consumed, on a molar basis, was about 71%. Inanother operation at thesame pressure and ata temperature of 290 C.,while the percent conversion of benzene to phenol per pass was reducedto about 0.5% on a molar basis, the yield of phenol based on the mols ofbenzene consumed was still of the order of 70%. In the last mentionedoperation, the reactant feed was about 13 gram mols per hour and thecomposition of the gasiform reactant feed, by volume, was 30.5% benzene,20% sulfur dioxide, 10% oxygen and 39.5% nitrogen.

In still another operation at 270 p. s. i. g. pressure and a temperatureof 550 C., a conversion per pass of benzene to phenol of about 5.5%, on

a molar basis, was secured, the yield of phenol on the benzene consumedbeing about 60%, also on a molar basis. In this operation, the reactantfeed was 12.3 gram mols per hour and the composition of the gasiformfeed was, by volume, approximately 28% benzene, 19.5% sulfur dioxide,10.5% oxygen and 42% nitrogen. Diphenyl was noted in the reactionby-products.

. Example 2 In an operation conducted at a pressure of p. s. i. g. and atemperature of 360 C., using the same catalyst and reaction tubedescribed in Example 1, a conversion per pass of benzene to phenol ofabout 7 on a molar basis was secured with a yield of phenol on thebenzene consumed of about 55%, on a molar basis. In this operation, thereactant feed amounted to 15.3 gram mols per hour and the composition ofthe gasiform feed was about 24% benzene, 16% sulfur dioxide, 12% oxygenand 48% nitrogen on a volume basis.

In a similar operation conducted at 230 0.. the percent conversion per.pass on a molar basis was reduced to about 1%, but the yield of phenolon the benzene consumed still amounted to approximately 72% on a. molarbasis. In this operation, the feed was about 15.5 gram mols per hour andthe composition of the feed gas was about 24% benzene, 17% sulfurdioxide, 12% oxygen and 47% nitrogen on a volume basis.

Example 3 In an operation carried out at 270 p. s. i. g. pressure and ata temperature of 565 C., the adsorptive material employed was alumina of4 to 8 mesh with noadded metal salts. The reaction tube was of the samesize as in Example 1 andcontained' 15 .ml. of alumina. The

I. rate of totai reactautfeed was 13.4 gram mols hour and the reactantfeed gas contained, by volume, 33.7% benzene, 11.1% sulfur dioxide,11.0% oxygen, and 44.2% nitrogen. The percent conversion perpass ofbenzene to phenol was about 4.2% on a molar basis and the yield ofphenol on the basis of benzene mols consumed was about 32.5%. Underthese conditions, an appreciable quantity of diphenyl was also formed.

Similar operations were conducted at various temperatures as low as 400C. with effective yields of phenol.

The proportion of carbon dioxide in the gaseous effluent from thereactor will vary but in themore efficient operations, it is found that,in general, it is below about by volume. Usually, the oxygen contentof'the reaction eflluent gas is less than 3% by volume and, in moreefficient operations, less than 1% by volume. Small amounts of carbonmonoxide may be found in the gases leaving the reaction zone.

In the foregoing examples, nitrogen was used as the inert gas. Carbondioxide has also been employed as the inert gas with approximately thesame results as when using nitrogen, but with some indication of arepression of carbon dioxide formation in the reaction zone.

In carrying out the process of the invention with a homolog of benzenehaving an aliphatic side chain, such as toluene or xylene, it is foundthat in addition to the corresponding phenolic compounds, some aromaticaldehydes and carboxylic acids are produced. Thus, toluene yields notonly cresols, principally metacresol, but also some benzaldehyde andsome benzoic acid.

Within the reaction temperature range herein set forth, at the highertemperatures, higher conversions of aromatic hydrocarbon per pass areachieved. At lower temperatures, lower conversions per pass are ingeneral secured, although this may be modified by the operatingpressure, since at higher pressures, higher conversions are obtained.Sometimes, a lower reaction temperature and, hence, lower conversion perpass are selected to attain a. higher .total yield of oxygenated productbased on the mols of aromatic hydrocarbon consumed. In operating undersuch conditions, the unreacted aromatic hydrocarbon and sulfur dioxideare obviously recycled to the reactor and the problem of closelycontrolling the reaction temperature is clearly facilitated because ofthe limited reaction which is taking place in the gasiform streamflowing through the reactor.

The preferred metallic catalyst promoters of the adsorptive contactmaterials which may be used in the process of this invention are'saltsof cobalt, copper, iron, vanadium and uranium. A cobalt saltsupplemented by a small proportion of a silver salt is a particularlyeffective metallic catalyst promoter.

Where the process of the invention is conducted in the presence ofparticulate adsorptive material on a large scale, it is advantageous touse relatively fine particles, say all passing through a 60-mesh screen,and to maintain the particulate mass in a well fluidized condition.Fluidization greatly increases the rate of heat transfer to coolingsurfaces in contact with the particulate mass and facilitates themaintenance of the desired reaction temperature uniformly".

throu hout the particulate mass. Fluidization' is the technique-by whichan upwardly flowing gas tream is brought into intimate contact with amass or finely divided solid particles at such a velocity that the solidparticles become suspended inthe gas but exhibit slippage or hinderedsettling" in the upwardly flowing gas. A fluidized mass of solidparticles is characterized by turbulence and random motion of theparticles and gives an appearance resembling that of a body of boilingliquid.

As a further guide in producing aromatic oxygenated products inaccordance with this invention, it is observed that the space velocityof the reactant gaseous stream flowing through the reaction zone,expressed as volumes of gas per volume of reaction zone per hour, inwhich expression the gas is measured at reaction temperature andpressure, is generally of the order of 7000 and higher. Space velocitiesin the range of about 10,000- to 20,000 are frequently verysatisfactory.

Although the present invention has been described in connection with thedetails of various specific embodiments thereof, it will be understoodthat the invention is not to be regarded as limited to such detailsexcept insofar as included in the accompanying claims.

I claim:

1. The method of effecting limited oxidation of aromatic hydrocarbonswith formation of phenols which comprises reacting in vapor phase anaromatic hydrocarbon with oxygen in the presence of a volume of sulfurdioxide at least equal to the volume of said oxygen in a reaction zonemaintained at a temperature in the range of about 230 to 600 C., andwithdrawing from said reaction zone gasiform reaction effluentcontaining phenol thus formed.

2. The method of claim 1 wherein the reaction is conducted in contactwith a solid adsorptive material.

3. The method of claim 2 wherein the adsorptive material is activatedalumina.

4. The method of claim 2 wherein the adsorptive material comprises ascatalyst promoter a compound of a metal of the class consisting of thetransition elements and the elements of the ID group of the periodictable.

5. The method of claim 4 wherein the catalyst promoter is a cobaltcompound supplemented by a silver compound.

6. The method of producing a phenol by the oxidation of an aromatichydrocarbon which comprises introducing into a reaction zone maintainedat a temperature in the range of about 230 to 600 C. a, gasiformreactant mixture comprising said aromatic hydrocarbon, oxygen and sulfurdioxide, the concentration of oxygen in said mixture being within therange of about 2% to 20% by volume and the concentration of sulfurdioxide being at least as great as that of oxygen, and withdrawing fromsaid reaction zone gasiform reaction effluent containing phenol thusproduced.

'7. The method of claim 6 wherein the reaction zone is maintained at apressure of about to 300 p. s. i. g.

8. The method of claim 6 wherein the reac tion zone contains a contactmass of solid adsorptive material.

9. The method of claim 8 wherein the solid adsorptive material comprisesas catalyst promoter a compound of a metal of the class consisting ofthe transition elements and the elements of the Ib group of the periodictable.

l0. The method of producing a phenol by the ox1dation of an aromatichydrocarbon which comprises introducing into a reaction zone mainsolidsolid tained at a temperature in the range of about 350 to 550 C. agasiform reactant mixture comprising said aromatic hydrocarbon, oxygenand sulfur dioxide, the concentration of oxygen in said mixture beingwithin the range of about 2% to 20% by volume and the concentration ofsulfur dioxide being at least as great as that of oxygen, andwithdrawing from said reaction zone gasiform reaction efiluentcontaining phenol thus produced.

11. The method of claim 10 wherein the arc-- matic hydrocarbon isbenzene.

12. The method of claim 10 wherein the aromatic hydrocarbon is toluene.

13. The method of claim 10 wherein the reaction zone contains a contactmass of solid adsorptive material.

14. The method of claim 10 wherein the concentration of oxygen is withinthe range of about 5% to by volume and the concentration of sulfurdioxide is of the order of 1.5 times that of oxygen.

15. The method of claim 14 wherein the reaction zone contains a contactmass of silica gel.

16. The method 01' producing phenol by the oxidation of benzene whichcomprises introducing into a reaction zone maintained at a temperaturein the range of about 230 to 600 C. a gasiform reactant mixturecomprising said benzene, oxygen and sulfur dioxide, the concentration ofoxygen in said mixture being within the range of about 5 to 10% byvolume and the concentration of sulfur dioxide being at least as greatas that of oxygen, and withdrawing from said reaction zone gasiformreaction effluent containing phenol thus produced.

17. The method of claim 16 wherein the reaction zone contains a contactmass of activated alumina.

18. The method of claim 17 wherein the contact mass is maintained in afluidized condition.

19. The method of claim 16 wherein the reaction zone contains a contactmass of solid adsorptive material comprising as catalyst promoter acompound of a metal of the class consisting of the transition elementsand the elements of the Ib group of the periodic table.

WILLIAM H. REEDER III.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,855,486 Morrell et a1 Apr. 26, 1932 2,223,383 Moyer et al.Dec. 3, 1940 2,373,008 Becker Apr. 3, 1945 2,456,597 Schlesman Dec. 14,1948

1. THE METHOD OF EFFECTING LIMITED OXIDATION OF AROMATIC HYDROCARBONSWITH FORMATION OF PHENOLS WHICH COMPRISES REACTING IN VAPOR PHASE ANAROMATIC HYDROCARBON WITH OXYGEN IN THE PRESENCE OF A VOLUME OF SULFURDIOXIDE AT LEAST EQUAL TO THE VOLUME OF SAID OXYGEN IN A REAC-